The present invention relates to a regulator for a sine wave generator and more specifically for a generator having to provide a high power and low distortion current sine wave, for instance to an antenna supplying an electromagnetic field in order to have it captured and processed by a transponder. It also relates to a current sine wave generator unit including such a regulator, which is more specifically adapted to provide a high power and low distortion sine wave with a constant AC amplitude on a variable load, this load being the antenna itself in the above mentioned application.
As already known, the slope of the start-up envelope and the slope of the shut-off envelope of a generated sine wave need to be tightly controlled.
According to a known solution, a regulator is associated to the sine wave generator in the sine wave generator unit and a power bridge links the generator to the load in order to provide the required sine wave with a determined power. The output of the power circuit is driven, according to a determined envelope, by means included in and/or associated to the regulator.
For instance, a third order low-pass filter, included in the regulator, is connected to a sensing output of the power bridge, which provides a feedback sense signal in relation with the sine wave provided from the power bridge to the load. A comparator, usually a comparison amplifier, is included in the regulator; it receives separately the sense signal and a set point signal corresponding to the determined envelope. A set signal, obtained at an output of the comparator, is applied to a control input of the sine wave generator as a regulation signal.
However, unacceptable delays are obtainable with this type of regulator including a third order low-pass filter. There is a risk of clamping at the level of the comparison amplifier, if the set signal during for instance start-up phase becomes inappropriately high. In such conditions, the regulation feedback loop of the current sine wave generator unit does not remain as stable as required and it becomes prone to relaxation problems.
An object of this invention, therefore, is to provide a regulator for a sine wave generator unit, and more specifically to a generator unit providing a high power and low distortion output sine wave, including a load feeding power-bridge connected to an output of a sine wave generator, said regulator being inserted between a feedback output of the power-bridge and a reference voltage input of the sine wave generator, said regulator including regulation means providing a power regulation signal to the reference voltage input of the sine wave generator from a comparison between a signal at the feedback output of the power bridge and a predetermined set point signal.
According to the invention, this regulator is a proportional integrating differentiating regulator including start-up and/or shut-off envelope controlling means associated to regulation means for obtaining a tightly controlled start-up and/or shut-off slope(s) of the signal at the load feeding output of the power bridge in addition to a tight control of the signal envelope between a start-up slope and the following shut-off slope.
In a preferred embodiment, the regulation means includes:
a comparing amplifier which receives the feedback signal from the controlled power bridge and a predetermined set point signal corresponding to a constant voltage for controlling the signal envelope between start-up and shut-off by means of a first current source;
start-up controlling means including a second current source in series with a capacitor which is in parallel with the first current source;
shut-off controlling means including a third current source also in parallel with the first current source for providing a control output signal at the level of a terminal common to the three current sources and to the capacitor.
The invention also extends to a sine wave generator unit and more specifically sine wave generator unit providing a high power and low distortion output sine wave, which includes a load feeding power bridge connected to an output of a sine wave generator and a regulator inserted between a feedback output of the power-bridge and a reference voltage input of the sine wave generator, said regulator including regulation means providing a power regulation signal to the reference voltage input of the sine wave generator from a comparison between a signal at the feedback output of the power bridge and a predetermined set point signal.
According to the invention the sine wave generator unit comprises a proportional integrating differentiating regulator including start-up and/or shut-off envelope controlling means associated to regulation means for obtaining a tightly controlled start-up and/or shut-off slope(s) of the signal at the load feeding output of the power bridge in addition to a tight control of the signal envelope between a start-up slope and the following shut-off slope, as well as a first order band-pass filter for transmitting the feedback signal from the controlled power bridge to the comparing amplifier, with a level similar to the constant level of the predetermined set point signal.